In the preparation of photographic compositions, such as silver halide emulsions and coating compositions, which are aqueous systems, it is often desirable to add essentially water-insoluble, hydrophobic, photographically useful compounds (such as spectral sensitizing dyes and the like) to produce the desired photographic characteristics. One well known method to incorporate these hydrophobic compounds is to prepare a solution of the compound in a volatile, water miscible organic solvent and subsequently adding the solution to the emulsion or coating composition. Typically these solvents are methanol, ethanol, n-propanol, acetone, and the like. However, it is also generally recognized that use of these solvents can have several adverse consequences, specifically:
1. evaporation during handling can cause changes in concentration; PA1 2. the solvents can interact with other components to form solid particles leading to coating defects; PA1 3. use of these solvent requires extra expense to provide worker safety (from vapors and splashing); and PA1 4. the solvents are evaporated during coating and represent an organic vapor emission, which can be undesirable. PA1 (a) mixing particles of the photographically useful compound with particles of a hydrophilic solid material; PA1 (b) heating the resulting mixture in a primary processing device to at least the softening point of the mixture, and expelling the heated mixture directly from the primary processing device to rapidly cool the mixture and to thereby directly form a solid additive material having a specific surface area of at least about 10 square centimeters per gram; and PA1 (c) adding the solid additive material directly into the aqueous photographic composition. In the method of this aspect of the invention, step (b) is preferably carried out in an extruder or melt spinning device. PA1 (a) mixing particles of the hydrophobic compound with particles of a hydrophilic solid material comprising a mixture of water soluble polymer and a water soluble low molecular weight compound having a melting point between about 30.degree. C. to about 200.degree. C.; PA1 (b) heating the resulting mixture in a primary processing device to at least the softening point of the mixture, and expelling the heated mixture directly from the primary processing device to rapidly cool the mixture and to thereby directly form a solid additive material having a specific surface area of at least about 10 square centimeters per gram; and PA1 (c) adding the solid additive material directly into the aqueous medium. In the method of this aspect of the invention, step (b) is preferably carried out in an extruder or melt spinning device. PA1 (a) derivatives, particularly alkyl derivatives, of urea and thiourea, preferably those of the formula ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each independently represent alkyl having 1 to 4 carbon atoms, optionally substituted by hydroxyl, cycloalkyl or phenyl; tolyl, which is optionally substituted with OH- groups; and wherein R.sub.1, R.sub.2 and R.sub.3 can also be hydrogen; and Z represents oxygen or sulphur. The following examples may be given: N-ethylurea, N-butylurea; N-(3-tolyl)-urea, N,N', -N,N'-ethyleneurea, N-methylthiourea, N, N'-dimethylthiourea, N-ethyl-N-phenylurea and N-hydroxymethylurea. PA1 (b) saturated and unsaturated mono- and dicarboxylic acid amides, particularly those of formula EQU R--CO--NH.sub.2 or R--(CONH.sub.2).sub.2 PA1 wherein R represents an alkyl or alkylene radical having 1 to 6 carbon atoms, or the group --CH.dbd.CH--, CH.sub.2 .dbd.CH-- or CH.sub.3 CH.dbd.CH--, also phenyl or tolyl, also heterocyclic saturated and/or unsaturated 5- or 6-membered ring having at least one N, O, S, CO or NH in the ring, whereby the symbol R can optionally be substituted also by OH, NH.sub.2, halogen or hydroxyalkyl having 1 to 3 carbon atoms. The acid amides are, for example, acetamide, chloroacetamide, nicotinic acid amide and benzamide. PA1 (c) lactams such as d-valerolactam, e-caprolactam and oenantholactam; PA1 (d) acid imides or derivatives of acid imides, especially those of the general formula ##STR2## wherein A represent --CH.dbd.CH-- or (CH.sub.2).sub.n, wherein n is 1 to 6, and A can optionally be substituted by OH, NH.sub.2, halogen, hydroxyalkyl (C.sub.1 --C.sub.3), examples of these are: succinimide, maleinimide and N-hydroxysuccinimide; PA1 (e) oximes such as acetoneoxime, cyclohexanoneoxime and diacetylmonoxime; PA1 (f) saturated and unsaturated 5- or 6-membered heterocyclic compounds which contain in the ring O, S, CO and NH, and which can optionally be substituted with OH, NH.sub.2, halogen, alkyl (C.sub.1 --C.sub.3) groups, such as symmetrical trioxane, imidazole, 2-methyl-imidazole, pyrazole, pyrazine, 2,3-dimethyl-1-phenyl-5-pyrazolone, and 1,2,4-triazole; PA1 (g) aliphatic or aromatic, polyvalent alcohols, such as 2,2-dimethyl- and 2,2-diethylpropanediol-1,3; dihydroxyacetone, o-xylylene glycol, erythrite, D-fructose, maltose, xylite, sorbitol and mannitol; PA1 (h) polyalkylene glycols, such as polyethylene glycol preferably having a molecular weight of 1,000 to 20,000, especially those of the formula ##STR3## wherein R represents a saturated or unsaturated alkyl radical having 9 to 30 carbon atoms, and n and m each represents the numbers 3 to 200; PA1 (i) carbamic acid esters, such as carbamic acid methyl ester, carbamic acid ethyl ester and carbamic acid propyl ester. PA1 (j) derivatives of benzene, particularly those of the general formula ##STR4## wherein A, B, C and D each independently represent OH, halogen, alkyl, hydroxyalkyl and alkoxy having 1 to 3 carbon atoms; and wherein A, B and C can be hydrogen; the following may for example be mentioned; 1,4-dihyroxybenzene 2,6-dihydroxytoluene, 2,3-dihydroxytoluene, 2,4-dimethyl-1,5-dihydroxybenzene, 4,5-dimethyl1,2-dihydroxybenzene, 3,5-dimethyl-1,2-dihydroxybenzene, 1,2-bis-(hydroxymethyl)-benzene, 1,3-bis(hydroxymethyl)-benzene, 1,4-bis-(hydroxymethyl)-benzene, 2-chloro-1,4-dihydroxybenzene, 4-chloro-1,2-dihydroxybenzene, 1-chloro-2,4,-dihydroxybenzene, 1-chloro-3,5-dihydroxybenzene, 1-chloro-2-5-dimethyl-1,4-hydroxybenzene and 1-chloro-4,5-dimethyl-2-hydroxybenzene.
Others have recognized these problems and have attempted various methods of eliminating volatile organic solvent solutions as an incorporation method. However each of the methods developed to date have significant problems associated with them as described below.
Boyer and Caridi in U.S. Pat. No. 3,676,146 disclose a process of dispersing spectral sensitizing dye in a water soluble organic liquid and subsequently adding the mixture to a silver halide emulsion. Prior to addition to the emulsion, the dye-solvent dispersion can be added to a gelatin solution. This process requires preparation of a slurry or dispersion (by ball milling) then subsequent addition of a gelatin solution and then drying. This is a relatively complicated process that can result in significant process time and materials losses especially when compared with the current practice of preparing a volatile organic solvent solution described above.
In U.S. Pat. No. 4,140,530, Trunley and Hopwood disclose a process of creating a solid additive mixture containing a hydrophobic photographic compound. The mixture is prepared by mixing the hydrophobic compound with a water soluble organic powder then adding a hydrophilic binder solution (such as gelatin) and, optionally, a solid wetting agent to form a paste. Noodles are then created from the paste and then dried. After removing water in the drying step, the solid noodles are added to the silver halide emulsion or coating composition. In a similar process, U.S. Pat. No. 4,146,399 describes adding another process step to compress the noodles into uniform tablets. Relative to the current practice of preparing an organic solvent solution, the processes described in U.S. Pat. Nos. 4,140,530 and 4,146,399 require numerous process steps which invariably cause additive waste and complicate the manufacturing process. In addition, in U.S. Pat. No. 4,146,399, addition of an amount of material other than unit tablet quantities would be inconvenient.
Trunley and Hopwood also disclose in U.K. Patent No. 1,563,133 a process of creating a solid additive mixture by first melting a water soluble organic compound and either dissolving or dispersing the photographic additive in the molten organic compound. The mixture is then cooled and solidified. The solid mixture is then ground to a fine powder and added to the silver halide emulsion or coating composition. Grinding the mixture adds another process step (where physical losses can occur) and creates the problem of powder dusting when the mixture is added to the liquid emulsions or coating compositions.
In European Patent Application 468 389 A1, Mason describes a process of placing a hydrophobic photographic additive as a powder in a gelatin capsule in an effort to avoid the problems of powder dusting. The gelatin capsule is then added to the silver halide emulsion or coating composition. This method, although overcoming the potential powder dusting problem disclosed in U.K. Patent 1,563,133, does make addition of additive quantities intermediate between the unit capsule quantities difficult, especially if the noncapsuled photographic additive does not wet and disperse well after addition to the emulsion or coating composition surface.
In U.S. Pat. No. 5,096,492 to Fuisz, a method of dispersing an oleaginous substance in aqueous medium is disclosed. In the method of Fuisz, the oleaginous substance is mixed with a saccharide, such as sucrose, and the resulting mixture is melt spun in a cotton candy spinning machine or the equivalent. The resulting product disposes autogeneously in water to form a colloidal-like dispersion. It has been found that certain hydrophobic compounds and certain mixtures of hydrophilic compounds and hydrophobic compounds require higher temperatures and/or longer residence times in the melt spinning machine which can lead to oxidation or burning of the material. Also, when certain hydrophobic compounds are used in the Fuisz method a non-uniform dispersion is obtained. We believe this to be due to inadequate dissolution or dispersal of the hydrophobic compound in the saccharide.